In computers, many datalinks are used to conduct data communications between various devices composing its system. Recently, a serial datalink that a parallel signal is converted into a serial signal by time-division multiplexing and then transmitted is widely used since it has merits that the cable numbers can be reduced and the skewing between channels as in the case of a parallel datalink does not occur. In general, in the serial datalink, a certain signal continues to be transmitted to obtain the bit synchronization or frame synchronization of a receiver even when there is no packet to be transmitted. For example, in the Fibre Channel(ANSI X3T11, Fibre Channel Physical and Signaling Interface Rev.4.3, 1994) which is a standard of datalinks for connecting peripheral equipments, an idle signal continues to be transmitted when there is no packet(or frame in the Fibre Channel). In the Fibre Channel, to distinguish a packet from an idle signal, Start of Frame and End of Frame delimiters are added to the start and end, respectively, of the packet.
On the other hand, to detect an error during data transmission in a computer, a parity signal, which is added in the proportion of one bit to one byte data, is often used. For example, if the number of 1 in one byte data is odd, then the parity signal is 1, or, if the number is even, then the parity signal is 0.
These techniques can be applied not only to a datalink with point-to-point connection but also to a network with a switch. The aforementioned Fibre Channel has also definitions for the standards of a star network which are provided with a switch called Fabric and a loop network other than point-to-point connection. However, these networks are not different from the point-to-point connection in that delimiters are added before and after a packet.
However, in the conventional techniques, there is a problem that the overhead is increased due to the addition of the delimiters and the latency of a datalink is thereby increased. For example, in the Fibre Channel, since both the Start of Frame and End of Frame delimiters have one word(40 bits) length, the data reception is so much delayed. Especially in the datalink for interconnecting between processors or memories in the parallel computer, the increase in latency is a serious problem since it causes the degradation of system performance.
On the other hand, when the parity signal is added to data, the transmission capacity of a datalink needs to be so much increased. Especially in the serial datalink, in order to increase the transmission capacity, the number of channels to conduct the parallel-to-serial conversion needs to be increased, therefore costing more. For example, though data itself needs only 8-to1 parallel-to-serial conversion, the parity-added data needs 9-to1 parallel-to-serial conversion. Since the 9-to1 parallel-to-serial conversion is not in common use, the cost will be highly increased. Meanwhile, since even the Fibre Channel does not support the parity transmission, some means for transmitting the parity needs to be provided.
These problems exist not only in a point-to-point datalink but also in a network.